The invention relates to an arrangement in a rock drilling apparatus comprising a feed for feeding a rock drill during the drilling; at least one rear support connected to the feed substantially parallel to and rearward of the feed, the support being moveable by its own support cylinder to rest on a surface rearward of the feed; and means for supplying pressure fluid to the support cylinder.
When holes are drilled in rock, the drill apparatus is usually supported by hydraulically-driven supports at its front and/or rear end. When the drill apparatus is directed, it is first adjusted in the correct direction, and the supports are then moved outward at the end of the drill apparatus by hydraulic cylinders until the supports rest against a surface in that direction. This is usually done before the drilling is started, and the bracing is usually not corrected in any way. During the drilling both the vibration and the feed capacity of the rock drill typically make the supports sink in the support surface, for example as the chippings in the surface yield. As a result, the direction of the drill apparatus changes and has to be corrected, which is at present usually performed by different angle gauges and very often by automatic adjustment.
In extension rod drilling, it is of prime importance to keep the direction during the drilling. Even a minor lateral change or change of angle to the effect that the drill axis of the drill apparatus and the centre axis of the hole do not coincide causes problems, for example, as regards disassembly of the drill equipment, since the threaded joints of drill pipes then no longer open in the correct order. A directing error of even half a degree is known to hinder automatic disassembly of the drill equipment. Another drawback resulting from the known methods of adjustment is that the drill apparatus, although in correct direction, is displaced laterally from the axis of the drill hole, which causes similar problems.
U.S. Pat. No. 5,129,464 teaches a solution in which the anchoring force of the feed of a rock drilling apparatus against a rock surface is to be maintained constant by adjusting the force that pushes the feed in proportion to the feed force of the rock drill in such a way that the difference of the forces and thereby the anchoring force remain constant. The solution does in no way eliminate the above problem concerning the changing of the direction and the resulting change of direction or lateral displacement that make it more difficult to disengage the drill rods.